Cancer accounts for nearly one quarter of deaths in the United States, exceeded only by heart diseases. In 2006, there were 559,888 cancer deaths in the US (National Center for Health Statistics: 2009). Although recent advances have increased our understanding of some of the mechanisms leading to cancer, to this day, finding effective treatments for cancer is a major challenge among researchers. Cancer is now primarily treated with one or a combination of three types of therapies: surgery; radiation; and chemotherapy. Surgery involves the bulk removal of diseased tissue. While surgery is sometimes effective in removing tumors located at certain sites, for example, in the breast, colon, and skin, it cannot be used in the treatment of tumors located in other areas, such as the backbone or brainstem, nor in the treatment of disseminated neoplastic conditions such as leukemia. Radiation therapy involves the exposure of living tissue to ionizing radiation causing death or damage to exposed cells. Side effects from radiation therapy may be acute and temporary, while others may be irreversible. Chemotherapy involves the disruption of cell replication or cell metabolism. It is used most often in the treatment of breast, lung, and testicular cancer. One of the main causes of failure in this treatment of cancer is the development of drug resistance by cancer cells, a serious problem that may lead to recurrence of the disease or even death.
Hypoxia, a characteristic of solid tumors, can pose a major hindrance to effective solid tumor therapy. It is characterized by a reduction in the partial oxygen pressure in cells or tissue. Oxygen can diffuse 100-180 μM from the end of the nearest capillary to the cells before it is used up completely (Powis and Kirkpatrick, 2004, Mol Cancer Ther., 3:647-654). Therefore, in solid tumors, when the existing vascular system is unable to supply the growing tumor with adequate amounts of oxygen, it results in hypoxia, low pH and lack of sufficient nutrients (Denko, 2008, Nat Rev Cancer, 8:705-713; Pouyssegur et al., 2006, Nature, 441:437-443). Tissue oxygen electrode measurements taken in cancer patients have shown a median range of oxygen partial pressure of 10 to 30 mmHg, with a significant proportion of readings below 2.5 mmHg, whereas those in normal tissues range from 24 to 66 mmHg. (Vaupel, 1993 in Drug Resistance in Oncology. Teicher, (ed.) 53-85, Marcel Dekker, New York). Tumor hypoxia has been shown to reduce the effectiveness of radiation and chemotherapy (Harris, 2002, Nat Rev Cancer, 2:38-47; Brown and Giaccia, 1998, Cancer Res. 58:1408-1416). In the absence of oxygen, which is the most electro-affinic molecule in cells and reacts chemically with the fundamental biological lesion produced by ionizing radiation, radiotherapy is severely compromised in its ability to kill hypoxic tumor cells (Gray et al., 1953, Br J Radiol, 26:638-648). Hypoxia increases the progression of malignancy and metastasis by promoting angiogenesis (Hockel and Vaupel, 2001, J Natl Cancer Inst, 93:266-276; Harris, 2002, Nat Rev Cancer, 2:38-47). On the other hand, hypoxia (and possibly hypoxia-associated deficiencies in other nutrients such as glucose) can cause tumor cells to stop or slow their rate of progression through the cell cycle (Amellem and Pettersen, 1991, Cell Prolif, 24:127-141).
Because most anticancer drugs are more effective against rapidly proliferating cells than slowly or non-proliferating cells, this slowing of cell proliferation leads to decreased cell killing. Chemotherapy is further affected by hypoxia as chemotherapeutic drugs are delivered systemically. The diffusion of these drugs into the tumor decreases the exposure of the hypoxic regions to the drug as compared to oxygenated cells proximal to the vessels. Hypoxia also drives genetic changes in tumors such as loss or mutation of the p53 tumor suppressor gene. Moreover, the multidrug resistance (MDR1) gene product P-glycoprotein is induced by ambient hypoxia. (Comerford et al., 2002, Cancer Res, 62: 3387-3394). Finally, hypoxic regions are expected to be less amenable to immunotherapy due to their distance from nearby vessels and compromised lymphocyte function in a hypoxic environment. Tumor cells in this aberrant environment are therefore often resistant to radio- and chemotherapy (Brown and Giaccia, 1998, Cancer Res., 58:1408-1416).
Hypoxia Inducible Factor is the primary transcription factor activated by hypoxia and is responsible for orchestrating a number of cellular responses such as angiogenesis and glycolysis that help tumor cells adapt to hypoxic conditions (Greijer et al., 2005, J Pathol, 206:291-304). Over-expression of HIF-1 has been associated with increased patient mortality in several cancer types including breast, stomach, cervical, endometrial and ovarian cancers. See review by Quintero et al., J Cancer Sur., 2004, 30, 465-468. Tumor hypoxia and the expression of the hypoxia-inducible factor (HIF) family of proteins are also linked to poorer survival in patients with non-small cell lung cancer. See Jackson et al., Expert Opin Ther Targets, 2010, 14(10):1047-57.
HIF-1 activation and regulation is complex, with numerous points of potential inhibition. Clinical evidence has determined that expression of HIF-1 is strongly associated with poor patient prognosis (Brown and Giaccia, 1998, Cancer Res., 58:1408-1416). Active HIF is composed of alpha (HIF-1α, 2α) and beta (HIF-1β) subunits that dimerize and bind to consensus sequences (hypoxia responsive elements, HRE) in the regulatory regions of target genes. HIF controls the expression of more than 60 target genes whose products are critical to many aspects of tumor progression, including metabolic adaptation, apoptosis resistance, angiogenesis and metastasis. These include the Vascular Endothelial Growth Factor (VEGF), erythropoietin, glucose transporters, and glycolytic enzymes. In normoxia, HIF is hydroxylated and interacts with the von Hippel Lindau protein (pVHL), an E3 ubiquitin ligase subunit that targets HIF for degradation. In the absence of oxygen, HIF hydroxylation is inhibited, preventing binding to pVHL and leading to its intracellular accumulation. HIF-1 has been recognized as an important molecular target for solid tumor therapy due to its crucial role in tumor angiogenesis and progression.
A component of tumor growth is angiogenesis. Angiogenesis is a process by which new blood vessels are formed, and is essential in reproduction, development, and wound repair. Under these conditions, angiogenesis is highly regulated, so that it is turned on only as necessary, usually for brief periods of days, and then completely inhibited. However, many diseases are driven by persistent unregulated angiogenesis. For example, in tumor formation, angiogenesis is a critical step for tumor growth beyond a few mm2 and is associated with vascular leakiness and edema; in arthritis, new capillary blood vessels can invade the joint and destroy cartilage; and in diabetes, new capillaries can invade the vitreous humor, bleed, and cause blindness. VEGF, the most important known regulator of tumor angiogenesis is transcriptionally upregulated by HIF-1.
A number of research groups have identified compounds that can inhibit the HIF-1 pathway. These compounds affect HIF-1 levels by directly inhibiting HIF-1 signaling or by indirectly inhibiting signal pathways that affect HIF-1 expression. The mechanisms of action for HIF-1 inhibitors can involve reduction in HIF-1α mRNA levels or protein levels, HIF-1 DNA-binding activity or HIF-1 mediated transactivation of target genes. Compounds may also reduce protein levels by decreasing the rate of HIF-1α synthesis or by increasing the rate of HIF-1α degradation. A number of patent applications have provided small molecules based on a 2,2-dimethylbenzopyran scaffold for use in the treatment of hypoxia related pathologies (see e.g. WO 2004/087066 A2, WO 2007/025169 A2, WO 2010/006184 A2 and WO 2010/006189 A2). PCT Publication No. WO 2007/025169 A2 provides a range of small molecules characterized by aryl or heteroaryl moieties linked by a disulphide bridge as inhibitors to HIF-1. Hsp90 inhibitors, such as geldanamycin and its analogues can inhibit the HIF-1 pathway by binding to Hsp90 and interfering with its function as Hsp90 plays an important role in the stabilization of HIF-1α under hypoxic conditions (see Sato et al., 2000, Proc Natl Acad Sci USA, 97:10832-10837; Whitesell et al., 1994, Proc Natl Acad Sci USA., 91:8324-8328; Zhou et al. 2004, J. Biol. Chem. 279:13506-13513; Katschinski et al., 2002, J. Biol. Chem. 277:9262-9267 and Isaacs et al., 2002, J Biol Chem., 277:29936-44).
Inhibitors of topoisomerase such topotecan and a campothothecin analogue have also been identified as HIF inhibitors (Rapisarda et al., 2002, Cancer Res, 62:4316-4324; Rapisarda et al., 2004, Cancer Res, 64:1475-1482 and Rapisarda et al., 2004, Cancer Res, 64:6845-6848). It was determined that 2-methoxyestradiol inhibits tumor growth and angiogenesis by disrupting tumor microtubules (MTs) in vivo and inhibits HIF-1 induced transcriptional activation of VEGF expression (Mabjeesh et al., 2003, Cancer cell, 3:363-375). Thioredoxin inhibitors PX-12 and pleurotin have also been identified as inhibitors of HIF-1α and VEGF (Welsh et al., 2003, Mol Cancer Ther., 2:235-243). Echinomycin has been shown to affect HIF-1 DNA binding (Kong et al., 2005, Cancer Res, 65:9047-9055). PX-478 (S-2-amino-3-[4V—N,N,-bis(2-chloroethyl)amino]phenylpropionic acid N-oxide dihydrochloride) is a HIF-1 inhibitor that reduces HIF-1α protein levels (Welsh et al., 2004, Mol Cancer Ther, 3:233-244). The HIF-1 inhibitor DJ12 inhibits the binding of HIF-1 to DNA and prevents the activation of transcription (Jones and Harris, 2006, Molecular Cancer Therapeutics, 5:2193-2202).
Other mechanisms that decrease HIF-1α protein levels include inhibition of the cyclin dependent kinase by flavopiridol which also has an effect on VEGF (Newcomb et al, 2005, Neuro-Oncology, 7:225-235). Chetomin has been shown to be a disrupter of HIF by binding to p300, interfering with its interaction with HIF and inhibits tumor growth (Kung et al., 2004, Cancer cell, 6:33-43). The antifungal drug amphoteric B also inhibits HIF-1 leading to decreased recruitment of p300 (Yeo et al., 2006, Blood, 107:916-923). Another inhibitor includes the histone deacetylyase inhibitor, FK228, a bicyclic peptide, which has also been shown to inhibit HIF-1 activity under hypoxic conditions, as well as inhibit tumor angiogenesis (Lee et al., 2003, Biochem and Biophys Res Commun, 300:241-246).
Effective treatments for cancer are a major challenge among researchers and there is a need for new therapies targeting abnormal proliferative disorders. In particular, there is a need for new treatments that address hypoxia and its role in hyper-proliferative pathologies. It is thus the object of this disclosure to provide compounds and methods for treatment or prophylaxis of disorders characterized by abnormal cell proliferation. It is a further object of the disclosure to provide compounds and methods of treatment or prophylaxis of other disorders such as those leading to ischemia (e.g., stroke and ischemic heart disease), and non-cancerous angiogenic diseases such as rheumatoid arthritis and macular degeneration.